To deposit a metal or alloy from a suitable electrolyte solution, the article to be plated is connected as a cathode in the electrolyte solution. Direct current is introduced through an anode which consists of the metal or alloy to be deposited. In accordance with the first law of electrolysis, the weight of the deposit on the cathode is proportional to the product of the current density multiplied by the time of deposition. Accordingly, the rate of deposition is proportional to the current density. For example, silver will deposit at 10 .ANG./s at a current density of 1 mA/cm.sup.2, and this will rise to a 1 .mu./s at 1 A/cm.sup.2.
However, during electrodeposition, a diffusion layer of metal ions is created in the electrolyte solution adjacent the surface of the electroplated article. This diffusion layer results in decreasing the current density. To prevent the diffusion layer of metal ions from being formed, ultrasonic vibration is applied to the electrolyte solution between the article and the anode.
For example, U.S. Pat. No. 5,391,290 discloses a method of electroplating a metal strip moved through an electroplating tank with an acidic tin-electroplating solution. A plurality of ultrasonic vibrators are placed along the surface of an anode located near the bottom of the tank. The vibrators are connected to an external ultrasonic generator to cause the vibration of the anode, and hence the vibration of the acidic tin-electroplating solution between the anode and the metal strip. Thus, a diffusion layer of tin ions formed in the acidic tin-electroplating solution adjacent the surface of the metal strip is removed.
Another problem that needs to be solved during electroplating is caused by air bubbles adhered to the surface of an electroplated article when the article pretreated in various chemical solutions is immersed in an electroplating solution. The surface portions covered with the air bubbles cannot be processed by the electroplating solution, and hence, no material can be deposited on these portions. In the conventional electroplating system discussed above, the air bubbles cannot be removed from the surface of an electroplated article, because vibration applied to the electroplating solution would cause the air bubbles to be trapped beneath the article. Accordingly, the air bubbles adhered to the bottom surface of the article would not be eliminated. This problem becomes increasingly apparent when articles have complicated shapes, or viscous electroplating solutions are used.
Moreover, as discussed above, electroplating tanks in conventional electroplating systems are provided with complicated ultrasonic equipment that increases the cost of electroplating.
Therefore, it would be desirable to provide an ultrasonic system for removing air bubbles adhered to an article immersed in an electroplating solution.
Also, it would be desirable to provide an air bubble removal system that is low in cost and easily implemented.